Portable drilling machine

Abstract

A portable drilling machine wherein when a shorting failure occurs in a circuit part connected to a driving motor, this state is reliably detected and a false start of the motor is reliably prevented. A diving motor control circuit in the portable drilling machine includes a main control section; a triac and a relay which are connected to power supply terminals in series with the driving motor; peripheral circuits (a triac control circuit, a relay control circuit, a triac inspection and determination section, a bypass resistor, etc.) which are related to the triac and relay; and a current measurement section for measuring current flowing in the driving motor.

The invention claimed is: 
     
       1. A portable drilling machine comprising:
 a drive motor for rotationally driving a cutting tool; 
 a motor control unit for controlling actions of the drive motor; 
 a portable main body mounted with the drive motor and the motor control unit; and 
 a fixing unit for fixing the main body to a workpiece; 
 the motor control unit comprising: 
 a switching element and a relay that are connected in series with the drive motor to power-supply terminals; 
 a first resistor connected in parallel with the relay, connected in series with the drive motor, and connected in series with the switching element to the power supply terminals; 
 a first determining unit connected in parallel with the switching element, for determining whether the switching element has a short-circuit failure; 
 a switching control unit that provides switching control for the switching element to control a motor current flowing through the drive motor; and 
 an on-off control unit for controlling the relay, 
 wherein the relay is kept off during the determining by the first determining unit, and the relay is kept on in making the drive motor take rotational actions. 
 
     
     
       2. The portable drilling machine of  claim 1 , wherein
 the motor control unit comprises: 
 a current measuring unit that measures a current value of a current flowing through the drive motor; and 
 a second determining unit for determining whether the relay has a short-circuit failure. 
 
     
     
       3. The portable drilling machine of  claim 2 , wherein
 in the motor control unit immediately after fixing the main body to the workpiece by the fixing unit as a result of a power switch on for checking whether the relay has short-circuit failure, 
 the on-off control unit keeps the relay off, 
 the switching control unit subjects the switching element to a switching control at a desired duty, and 
 the second determining unit compares a current measurement value acquired by the current measuring unit with a predetermined reference value to issue a determination result depending on a result of the comparison. 
 
     
     
       4. The portable drilling machine of  claim 1 , wherein
 in the motor control unit while the drive motor normally rotates in response to a predetermined switching operation, 
 the on-off control unit keeps the relay on, and 
 the switching control unit subjects the switching element to a switching control at a desired duty. 
 
     
     
       5. The portable drilling machine of  claim 1 , wherein
 the drive motor is an AC motor, 
 the power-supply terminals are connected to an AC power supply, and 
 the switching element is a triac. 
 
     
     
       6. The portable drilling machine of  claim 1 , wherein
 the drive motor is a DC motor, 
 the power-supply terminals are connected to a DC power supply, and 
 the switching element is a transistor. 
 
     
     
       7. A portable drilling machine comprising:
 a rotation driving unit including a drive motor for rotationally driving a cutting tool; 
 a feed motor for advancing or retreating the cutting tool relative to the workpiece; 
 a motor control unit for controlling actions of the feed motor; 
 a portable main body mounted with the rotation driving unit, the feed motor, and the motor control unit; and 
 a fixing unit for fixing the main body to a workpiece; 
 the motor control unit comprising: 
 a switching element and a relay that are connected in series with the feed motor to power-supply terminals; 
 a first resistor connected in parallel with the relay, connected in series with the feed motor, and connected in series with the switching element to the power-supply terminals; 
 a first determining unit connected in parallel with the switching element, for determining whether the switching element has a short-circuit failure; 
 a switching control unit that provides switching control for the switching element to control a motor current flowing through the feed motor; and 
 an on-off control unit for controlling the relay, 
 wherein the relay is kept off during the determining by the first determining unit, and the relay is kept on in making the feed motor take rotational actions. 
 
     
     
       8. The portable drilling machine of  claim 7 , wherein
 the motor control unit comprises: 
 a current measuring unit that measures a current value of a current flowing through the feed motor; and 
 a second determining unit for determining whether the relay has a short-circuit failure. 
 
     
     
       9. The portable drilling machine of  claim 8 , wherein
 in the motor control unit immediately after fixing the main body to the workpiece by the fixing unit as a result of a power switch on for checking whether the relay has short-circuit failure, 
 the on-off control unit keeps the relay off, 
 the switching control unit subjects the switching element to a switching control at a desired duty, and 
 the second determining unit compares a current measurement value acquired by the current measuring unit with a predetermined reference value to issue a determination result depending on a result of the comparison. 
 
     
     
       10. The portable drilling machine of  claim 7 , wherein
 in the motor control unit while the feed motor normally rotates in response to a predetermined switching operation, 
 the on-off control unit keeps the relay on, and 
 the switching control unit subjects the switching element to a switching control at a desired duty. 
 
     
     
       11. The portable drilling machine of  claim 7 , wherein
 the feed motor is an AC motor, 
 the power-supply terminals are connected to an AC power supply, and 
 the switching element is a triac. 
 
     
     
       12. The portable drilling machine of  claim 7 , wherein
 the feed motor is a DC motor, 
 the power-supply terminals are connected to a DC power supply, and 
 the switching element is a transistor. 
 
     
     
       13. The portable drilling machine of  claim 1 , wherein
 in the motor control unit immediately after fixing the main body to the workpiece by the fixing unit as a result of a power switch on for checking whether the switching element has a short-circuit failure, 
 the switching control unit keeps the switching element off, 
 the on-off control unit keeps the relay off, and 
 the first determining unit issues a determination result that depends on magnitude of a voltage across terminals of the switching element. 
 
     
     
       14. The portable drilling machine of  claim 13 , wherein
 the first determining unit comprises: 
 a light-emitting element connected in parallel with the switching element; 
 a light-receiving element paired with the light-emitting element to make up a photo coupler; and 
 a binary signal generation circuit connected to the light-receiving element, for generating a signal having a first logical value when the light-receiving element is inactive and for generating a signal having a second logical value when the light-receiving element is active. 
 
     
     
       15. The portable drilling machine of  claim 14 , comprising a second resistor connected in parallel with the switching element and in series with the light-emitting element. 
     
     
       16. The portable drilling machine of  claim 1 , wherein
 the fixing unit has an electromagnet integrally incorporated in the main body, the fixing unit energizing the electromagnet when a power switch goes on to electromagnetically adhere to the workpiece, the fixing unit deenergizing the electromagnet when the power switch goes off to release electromagnetic adhesion.